Typical power amplifier (PA) technologies utilize multiple integrated circuits in order to provide functionality for amplification, power output control and for stabilization of the PA output signal level due to supply voltage and temperature fluctuations.
It is well appreciated to those skilled in the art of amplifier design that bias currents supplied to the RF signal amplification stages is are an important determinant of the performance of the amplification stages. For example, a bias current supplied to the base of a bipolar transistor acting as a RF signal amplification stage is a major determinant of the amplification performance demonstrated by that bipolar transistor. Selecting and supplying the correct bias current is crucial to optimizing the RF signal amplification characteristics of any transistor amplifier. Moreover, one can appreciate that having control over the bias current supplied to the transistor amplifiers can enable more sophisticated schemes for optimizing the power output characteristics of the transistor amplifier. For example, one might detect output power from a power amplifier and choose to modify the bias current in response to the measured output power. Furthermore, one can envisage other figures of merit associated with the performance of power amplifiers that might be optimized using control over the bias current, such as bias current reduction at lower output powers to improve operating efficiency when RF-induced rectification currents are low.
Of course, such a concept is not new to the art of power amplifier design or their utilization. Open-loop or close-loop control over the performance of a power amplifier through the bias current is well known to those of skill in the art. Moreover, closed loop control has been used to mitigate variations in power amplifier output power performance in response to input control voltages, external temperature changes, or simply to mitigate manufacturing tolerance.
Introducing a degree of control, however, over the performance of power amplifiers through the bias current entails using additional circuitry to convert voltage detection error signals into incremental base voltage changes on the transistors. That is, circuitry is required above and beyond the transistors used for providing RF signal amplification. For example, introducing control over the bias current will require, at a minimum, circuitry for receiving the control signal and for varying the bias current. Numerous circuit block architectures have been discussed in the prior art for achieving thereof.
Furthermore, all existing control architectures employ a substantial die area, and utilize multiple integrated circuit technologies with a net higher manufacturing cost and large associated packaging area. This traditional approach often results in a reduction in operating efficiency, due to the need for in-line coupling circuits, and poor repeatability of results, create more challenging calibration requirements and reduced manufacturing yields.
If is therefore an object of the invention to provide a power amplifier integrated circuit (PAIC) that overcomes the limitations of the prior art by fully integrating such bias and power control features on a single PAIC within a single manufacturing process technology. The PAIC advantageously realizes a reduced die and packaging area over existing solutions. Along with improved RF output signal power control repeatability versus temperature and supply voltage variations.